1. Field of the invention
This invention relates to an apparatus for the formation of images, such as electrophotographic copying machines, laser beam printers, etc.
2. Description of the prior art:
For example, a corona charger that is used to charge the photosensitive drum of an electrophotographic copying machine with electricity generally makes use of a tugsten corona wire extended within a box-shaped shield box. The box-shaped shield box has an opening for use in the corona charging, along the corona wire, so as to face the photosensitive drum, and corona charging takes place when high voltage is applied to the corona wire, resulting in a uniform charging of the photosensitive drum. In this way, when corona charging is done by means of the corona charger, Si-type gas such as silane (SiH.sub.4) contained in the surrounding gas form silicon compounds such as SiO.sub.2, etc., on the surface of the corona wire. These silicon compounds cause a steep decrease in the corona charging power of the corona wire, resulting in a lack of uniformity of the charging of the photosensitive drum by the corona charger and patches in the surface charge of the photosensitive drum, which causes difficulties in obtaining distinct images. For this reason, it is necessary to remove the silicon compounds attached to the corona wire regularly.
A cleaning apparatus for the corona wire has disclosed by, for example, Japanese Laid Open Utility Model Publication No. 60-68557, wherein the cleaning apparatus has a corona charger that can be removed from the body of the cleaning apparatus, and a corona wire cleaning means is attached to the body of the cleaning apparatus. In order to clean the corona wire, it is necessary to remove the corona charger from the body of the cleaning apparatus. In general, in image-forming apparatuses, the corona charger is fixed in place inside the body of the apparatus, so in such a case, the apparatus must be redesigned so that it is possible to remove the corona charger from the body of the apparatus so as to clean the corona charger. Even if as such a construction is made, it is very troublesome for the users of the image forming apparatus to remove the corona charger from the body of the apparatus just for the purpose of cleaning the corona wire. Also, in the cleaning apparatus disclosed in the Laid-Open Publication mentioned above, the corona wire is sandwiched into a part of the cleaning means in order to clean the wire. When external power is applied to the corona wire during the cleaning operation and the corona wire is pulled from where it is extended within the shield box, there is the possibility that the corona wire will be broken.